The present invention relates to a sharpening device for sharpening a rotating discoidal cutting tool. The invention also relates to a machine comprising such a device and, in particular, a severing machine for cutting off rolls of wound-up web material.
In many sectors of industry, machines are used for cutting materials of various types by means of discoidal cutting tools which rotate about their own axis. In particular, machines of this type are used in the paper and board converting industry and, in general, in the paper making sector.
In certain cases, the tools are used for the lengthwise cutting of a strip of paper material which is fed continuously, for example downstream of a board production plant, along the path on which the paper is wound into reels, or in other similar situations.
In the sector of the production of rolls of toilet paper, paper towels and other products in roll form, machines are used that are known as severing machines and have the function of cutting rolls or what are referred to as logs of great length transversely to their axis to reduce them to small rolls of dimensions corresponding to the dimensions of the finished product Severing machines of this type are described, for example, in EP-A-0 507 750, EP-A-0609 668 and U.S. Pat. No. 4, 041, 813.
In these various types of machine, it is necessary to undertake regular sharpening of the cutting edge of the cutting tool or tools. To this end, use is made of sharpening assemblies which normally comprise two grinders acting on the two flanks of the tool. The grinders may be motor-driven, for example by means of a hydraulic or pneumatic motor, or non-driven and rotated by friction by the movement of the cutting tool.
An object of the present invention is the production of a sharpening device for rotating discoidal cutting tools, in particular but not exclusively for web material, and especially material wound into rolls, which device is more efficient than the conventional devices.
Another object of the present invention is the production of a device of the abovementioned type which makes it possible to obtain more efficient sharpening and to lengthen the service life of the sharpening grinder or grinders.
These and other objects and advantages, which will be clearly apparent to those skilled in the art from a reading of the text that follows, are substantially achieved by means of a device for sharpening a rotating discoidal cutting tool, comprising at least one sharpening grinder, especially a rotating circular grinder, characterized by at least one dressing tool which interacts with the grinder to dress the working surface of said grinder, during the sharpening or between successive sharpenings of the cutting tool.
In this manner, the efficiency of the grinder and hence of the sharpening device is increased and better use is made of the grinder, its operating life being increased. Furthermore, the need to undertake manual dressing of the grinder, which would require the stopping of the sharpening device and, consequently, of the machine to which the device is fitted, is avoided. By avoidance of manual intervention, the serious risk of accidents caused by the closeness of the operator to the cutting tool is also avoided.
The grinder may be single or double for each tool. In the second case, the two grinders act on the two flanks of the cutting edge of the tool. In certain cases, it is also possible to provide two grinders on the same flank, acting on different portions of the flank of the tool, for example in order to obtain a cutting bevel of a particular shape. In all cases it is possible to provide, for each grinder or for only some of them, a dressing tool. For example, if two grinders are provided for each flank of the cutting tool, it is possible to provide a dressing tool for only one of the grinders or for both.
In a manner known per se, in accordance with a particularly advantageous embodiment of the device, the grinder or each grinder possesses a first actuator to move the grinder into an active position in which it acts on the cutting tool and into an idle position in which it is withdrawn from the cutting tool.
The dressing tool or each dressing tool preferably possesses a second actuator for moving said dressing tool alternately into an active position, in which it acts on said grinder, and into an idle position, in which it is withdrawn from the grinder.
With this arrangement, it is possible to move the grinder alternately into and out of operation, and the same can be done for the dressing tool, irrespective of the position of the grinder.
As mentioned above, the grinder or grinders may be motor-driven. According to a preferred embodiment, however, the grinder or grinders is or are supported on a non-driven shaft and are rotated by the action of friction when they come into contact with the rotating cutting tool. As regards the manner in which the grinders are motor-driven, also, if a plurality of grinders are provided in the same device they may all be non-driven, or motor-driven or some non-driven and some motor-driven.
When the grinder is mounted on a non-driven shaft, a rotation system may be associated therewith, facilitating the rotation thereof, in conjunction with the entrainment effect exercised by the cutting tool. For example, according to a possible embodiment, vanes fixed to the grinder may be provided, on which vanes acts a jet of air generated by one or more nozzles. The vanes and the nozzle or nozzles are oriented so as to urge the respective grinder to rotate in the same direction as that in which it is urged to rotate by the action of the cutting tool when the grinder is in contact with the latter.
This arrangement, or another appropriate system of rotation, makes it possible to obtain two results: on the one hand, dressing of the grinder is allowed even when the latter is not in contact with the cutting tool. This is particularly useful when the dressing operations have to be performed in whole or in part, with the grinder in the non-working position. Secondly, when the grinder is in operation, the system of rotation applies a driving torque to the grinder which is added to the torque deriving from the friction with the cutting tool and prevents the rotation of the grinder being stopped by the opposing torque applied by the dressing tool. If this were to happen during a sharpening operation it would cause the formation of steps in the working surface of the grinder.
In order to reduce or eliminate the scattering of chips caused by the sharpening and/or dressing, and also in order to avoid the risks of fire caused by the sparks given off during the sharpening phase, according to a particularly advantageous embodiment of the device, the grinder or grinders and the dressing tool or tools are accommodated in a containment housing. The housing is connected to a suction pipe and possesses a slit into which said cutting tool partially penetrates. This containment system may also be applied to a sharpening device without dressing tools. It is, however, advantageous in the case in which dressing tools are provided, in that, in this case, it is unnecessary to access the grinders at intervals in order to dress them and therefore the latter can be accommodated in a housing.
The invention also relates, in particular, to a severing machine for cutting rolls or logs of web material into small rolls, comprising at least one rotating discoidal cutting tool and an associated sharpening device, made as stated above.
More generally, the invention relates to, a cutting device comprising at least one rotating discoidal cutting tool and an associated device for sharpening said cutting tool, made as defined above.